1. Field of the Invention
The present invention relates to a liquid crystal display device. In particular, the present invention relates to a liquid crystal display device having a wide viewing angle.
2. Description of the Related Art
A display device includes a self-light emitting display device and a light receiving display device. A liquid crystal display device is the most typical light receiving display device. A driving method for liquid crystal in a liquid crystal display device includes a vertical electrical field type in which voltage is applied perpendicularly to a substrate and a horizontal electrical field type in which voltage is applied approximately parallel to the substrate. Each of a vertical electrical field type and a horizontal electrical field type has an advantage and disadvantage. For example, a horizontal electrical field type has characteristics such as a wide viewing angle, high contrast, high gradation display, and the like compared with a vertical electrical field type typified by a TN type, and is used for a monitor or television. These kinds of liquid crystal display devices coexist in the field of liquid crystal, and product development has been made. In addition, each of a liquid crystal material for a horizontal electrical field type and a liquid crystal material for a vertical electrical field type is developed and has different material characteristics according to a direction of applied voltage.
In addition, a horizontal electrical field liquid crystal display device includes an IPS (In-Plane Switching) type and an FFS (Fringe Field Switching) type. In an IPS type, a pixel electrode having a comb-shape or a slit and a common electrode having a comb-shape or a slit are alternately arranged and an electrical field approximately parallel to a substrate is generated between the pixel electrode and the common electrode, whereby a liquid crystal display device is driven (see Patent Document 1). On the other hand, in an FFS type, a pixel electrode having a comb-shape or a slit is placed over a common electrode which having a plane-shape that is formed in a whole pixel portion. An electrical field approximately parallel to a substrate is generated between the pixel electrode and the common electrode, whereby a liquid crystal display device is driven.
It is shown that an FFS liquid crystal display device has high transmittance, a wide viewing angle, low power consumption, and no crosstalk (see Non-Patent Document 1).
[Patent Document 1] Japanese Published Patent Application No. H9-105918
[Non-Patent Document 1] Ultra-FFS TFT-LCD with Super Image Quality and Fast Response Time, 2001 The Society For Information Display pp. 484-487
In a horizontal electrical field type liquid crystal display device which is typified by a conventional horizontal electrical field type liquid crystal display device, an electrical field applied to a liquid crystal material is not sufficient. This is because an electrical field is not well applied to a liquid crystal material which is right above a common electrode and a pixel electrode.
In addition, a wide viewing angle technique using a horizontal electrical field type such as an IPS type or an FFS type is used mostly for television; therefore, the technique is applied only to a transmissive type. However, a reflective type or a semitransmissive type is needed when reducing power consumption or outdoors use is required. However, a reflective or a semitransmissive type is realized by using a vertical electrical field type typified by a TN type.